1. Field of the Invention
The present invention relates to a turbo-molecular pump.
2. Description of the Related Art
Conventionally, there has been used a vacuum pump such as a turbo-molecular pump for chamber evacuation in a semiconductor manufacturing apparatus or a liquid crystal manufacturing apparatus, or the like.
A pump rotor of such a turbo-molecular pump is supported in a contactless manner by magnetic bearings and rotates at high speed. The pump rotor collides with process gas or the like and thereby has a high temperature. In view of this, in order to prevent breakage caused by creep deformation, the emissivity of the outer surface of the pump rotor or the emissivity of the outer surfaces of stationary blades and a cylindrical stator arranged around the pump rotor may be increased to increase the amount of heat release by radiation of the pump rotor.
In recent years, in an etching process performed by a semiconductor manufacturing apparatus or a liquid crystal manufacturing apparatus, the amount of reaction products adhered to a cylindrical stator of a vacuum pump increases, which may cause contact between a pump rotor of the vacuum pump and the reaction products. Further, an overhaul is required within a short period of time after starting the operation of the apparatus. Thus, there has been a need to make the temperature inside the pump (the temperature of a gas contact part) considerably higher than a conventional temperature to suppress adhesion of reaction products.
A method as disclosed in JP 3160504 B1 is known as a method of increasing the temperature inside a pump. In the invention disclosed in JP 3160504 B1, a heating target member (corresponding to a cylindrical stator of a screw groove pump member) which is arranged to face the outer periphery of a rotor cylindrical section of a pump rotor is directly heated.
In the invention as disclosed in JP 3160504 B1, the emissivity of the outer surface of the cylindrical stator and the emissivity of the outer surfaces of members around the cylindrical stator may be increased. In this case, when the temperature of the cylindrical stator is higher than the temperature of the members around the cylindrical stator, heat transfer by radiation from the cylindrical stator to the members around the cylindrical stator unnecessarily occurs. As a result, the temperature of the pump rotor may increase.
Therefore, there is desired a turbo-molecular pump that prevents accumulation of reaction products on a cylindrical stator and suppresses heat transfer by radiation from the cylindrical stator to members around the cylindrical stator.